High power semiconductor devices are increasingly deployed in demanding applications such as electric vehicles, power inverters, and high-frequency communications, where thermal performance is critical to long-term reliability. During operation, these devices are subjected to non-uniform temperature distributions, often resulting in steep thermal gradients across die and package interfaces. This study investigates the dominant thermal gradient-induced failure mechanisms in high power semiconductor components under real-world operational stress conditions. The research combines finite element thermal modeling, empirical thermal cycling, and failure analysis techniques—such as scanning acoustic microscopy (SAM), X-ray imaging, and cross-sectional electron microscopy—to evaluate material degradation and structural failures. Devices tested include power MOSFETs, IGBTs, and wide-bandgap devices (SiC, GaN), operating across a range of thermal profiles and duty cycles. Key findings reveal that thermal gradients contribute significantly to delamination at die-attach interfaces, crack propagation in solder layers, wire bond fatigue, and metallization erosion due to thermo-mechanical mismatch. These mechanisms are accelerated under cyclic power loading and high junction temperatures, where localized hotspots exacerbate stress concentration. Additionally, the study identifies threshold gradient levels above which failure rates sharply increase, offering predictive value for design and derating criteria. Mitigation strategies—such as optimized heat sink configurations, thermal interface materials (TIMs), and adaptive power cycling techniques—are evaluated for their effectiveness in reducing thermal-induced stress. The study contributes to the broader understanding of reliability engineering in power electronics and supports device design improvements aimed at enhancing thermal Robustness and operational lifetime.