In this paper, we study temperature-constrained hard realtime systems, where real-time guarantees must be met without exceeding safe temperature levels within the processor. Dynamic speed scaling is one of the major techniques to manage power so as to maintain safe temperature levels. As example, we adopt a simple reactive speed control technique in our work. We design a methodology to perform delay analysis for general task arrivals under reactive speed control with First-In-First-Out (FIFO) scheduling and Static-Priority (SP) scheduling. As a special case, we obtain a close-form delay formula for the leakybucket task arrival model. Our data show how simple reactive speed control can decrease the delay of tasks compared with any constant-speed scheme.