This paper presents the design, simulation, bench test and long-term reliability burn-in data of a drift-resistant clock Generator. Designed for applications at a stable body core temperature with a life-long operating expectancy, the relaxation oscillator uses multiple design techniques to minimize the long-term performance degradation, which results in a clock circuit with superior oscillating frequency stability. This design is implemented on a commercial CMOS process and bench test results shows the PSRR of this circuit is 0.25%/V. Long-term frequency drift data indicate that this oscillator has a less than 0.5% frequency drift over 100-year operating time at body core temperature.