This study examines how yield provision in stablecoins affects payment system stability and proposes regulatory design principles appropriate for the Korean market. The analysis is motivated by the growing use of rewards, interest-like payments, and decentralized finance services linked to stablecoin holdings. Although these arrangements may increase user benefits, they can alter the economic character of stablecoins by combining payment functionality with investment incentives. Because the associated risks depend on who provides the return, how it is generated, and what rights users obtain, this study distinguishes three forms of stablecoin yield provision: issuer-based yield, platform-based yield, and DeFi-based yield. The study adopts a theoretical and institutional policy-analysis approach based on prior research, regulatory materials, market practices, and a comparative review of the United States, the European Union, and Korea. Issuer-based yield refers to interest or an equivalent return paid directly by a stablecoin issuer and is generally linked to reserve-asset income. Platform-based yield is provided by exchanges, wallet providers, fintech companies, and other intermediaries that use deposited stablecoins for lending, liquidity provision, margin financing, or asset management. DeFi-based yield arises through smart contracts and on-chain protocols, often after users deposit stablecoins and receive tokens representing a yield-bearing position. Although platform-based and DeFi-based yields differ in their operational structures, both embed a payment asset in financial intermediation or investment activity. The analysis identifies five channels through which yield provision may affect payment system stability. First, it can increase run risk by shifting the motivation for holding stablecoins from transactional convenience toward return seeking. Yield-sensitive holders may respond rapidly to changes in interest rates, perceived risk, platform credibility, or expected returns. Under stress, this sensitivity may lead to coordinated withdrawals and redemptions, increasing liquidity pressure, reserve-asset sales, and depegging risk. Second, yield competition may strengthen risk-taking incentives. Issuers seeking to fund higher returns may increase the maturity or risk of reserve assets, while platforms may rely on leverage, maturity transformation, or risky lending. Third, losses and redemption pressure can be transmitted beyond individual issuers or platforms. Large-scale reserve liquidation may affect short-term funding markets, while collateral links, rehypothecation, margin calls, and forced liquidations may amplify shocks and transmit them to traditional financial markets. Fourth, yield provision may weaken the payment function of stablecoins. As balances become more responsive to returns and risk perceptions, payment-related liquidity may become less stable, and the distinction between a payment instrument and an investment product may become unclear. Fifth, yield-bearing stablecoins may interact with bank deposits, central bank digital currencies, financial intermediation, and monetary policy transmission by encouraging funds to migrate toward nonbank or offshore arrangements. The comparative analysis shows that major jurisdictions increasingly recognize these concerns, although their approaches differ. The European Union prohibits interest on asset-referenced tokens and e-money tokens under the Markets in Crypto-Assets Regulation and broadly covers benefits linked to token holdings. The United States prohibits payment stablecoin issuers from directly providing interest or yield under the GENIUS Act, while rewards offered by affiliates, exchanges, or other third parties remain a regulatory issue. Korea has not yet established a comprehensive framework for stablecoin yield provision. Existing rules focus mainly on virtual-asset user protection and unfair trading, while overseas stablecoins, exchange rewards, platform programs, and DeFi services remain accessible to Korean users. This regulatory gap requires a framework that addresses issuer conduct, functionally equivalent rewards, financial-intermediation activities, offshore providers, and personal-wallet transfers. Based on this analysis, the study proposes a function-based and risk-sensitive framework for Korea. Issuer-based yield on payment stablecoins should, in principle, be prohibited because it may undermine reserve safety, encourage yield-seeking asset management, and make payment stablecoins resemble unprotected deposits. Platform-based yield should not be governed by a uniform prohibition or permission. Regulation should distinguish rewards linked to actual payment or service use from returns paid merely for holding or depositing stablecoins. Where a platform conducts lending, maturity transformation, asset management, or other financial intermediation, enhanced requirements should apply, including authorization or registration, segregation of customer assets, liquidity and risk-management standards, disclosure of the source of returns, and controls on conflicts of interest. DeFi-based yield should be structurally separated from payment stablecoins and regulated as an investment product or high-risk financial service when it involves smart-contract risk, oracle risk, leverage, rehypothecation, or liquidity shortfalls. The study further emphasizes standardized risk disclosure, clear redemption terms, restrictions on misleading descriptions, and integrated supervision covering issuers, platforms, custodians, exchanges, and offshore access channels. These measures should be coordinated with Korea's electronic finance, banking, capital market, virtual-asset, CBDC, and monetary policy frameworks. The main contribution of this study is to treat stablecoin yield provision not as a peripheral product feature but as an institutional issue affecting payment infrastructure and financial stability. Because the analysis is primarily theoretical and institutional, future research should empirically examine liquidity volatility, redemption behavior, depegging risk, and the market-wide effects of platform-based and DeFi-based yield structures.