This study investigates the financial and governance effects of the 2021 merger that formed Bank Syariah Indonesia (BSI), applying the Risk Profile, Good Corporate Governance, Earnings, and Capital (RGEC) framework across two distinct periods: pre-merger (Q1 2019–Q4 2020) and post-merger (Q1 2021–Q4 2022). Using quarterly data from eight paired observations per indicator, the analysis combines descriptive statistics, Shapiro–Wilk normality tests, and Wilcoxon Signed-Rank tests to evaluate changes in Non-Performing Financing (NPF), Financing-to-Deposit Ratio (FDR), Good Corporate Governance (GCG), Return on Assets (ROA), Return on Equity (ROE), Operating Efficiency (BOPO), Net Operating Margin (NOM), and Capital Adequacy Ratio (CAR). The results reveal statistically significant improvements in asset quality, profitability, and operational efficiency (NPF, ROA, ROE, BOPO, NOM), a borderline decline in liquidity risk (FDR), and stable capital adequacy (CAR). GCG composites also improved descriptively. These findings demonstrate that the merger produced real operational and financial synergies while preserving prudential buffers. The study extends the resource-based and synergy theories to Islamic banking and offers practical insights for regulators, managers, and investors on how consolidation can strengthen systemic stability and bank performance in emerging markets.