In this paper, we present a low power high temperature 80C51 microcontroller. The low power optimizations are applied at gate and architectural level, by using extensive clock and data gating, and by completely redesigning the micro-architecture. We also present original clock gating techniques: pre-computed clock gating. To validate these techniques, extensive comparisons with other realizations of the same microcontroller are presented. It shows that gating techniques can achieve good performances.