The authors have carried out the large-signal characterization of silicon-based double-drift region(DDR) impact avalanche transit time(IMPATT) devices designed to operate up to 0.5 THz using a large-signal simulation method developed by the authors based on non-sinusoidal voltage excitation.The effect of band-to-band tunneling as well as parasitic series resistance on the large-signal properties of DDR Si IMPATTs have also been studied at different mm-wave and THz frequencies.Large-signal simulation results show that DDR Si IMPATT is capable of delivering peak RF power of 633.69mW with 7.95% conversion efficiency at 94GHz for 50% voltage modulation,whereas peak RF power output and efficiency fall to 81.08 mW and 2.01% respectively at 0.5 THz for same voltage modulation.The simulation results are compared with the experimental results and are found to be in close agreement. The authors have carried out large-signal characterization of silicon-based double-drift region (DDR) impact avalanche transit time (IMPATT) devices designed to operate up to 0.5 THz using a large-signal simulation method developed by the authors based on non -sinusoidal voltage excitation. the effect of band-to-band tunneling as well as parasitic series resistance on the large-signal properties of DDR Si IMPATTs have also been at at different mm-wave and THz frequencies. Larger-signal simulation results show that DDR Si IMPATT is capable of delivering peak RF power of 633.69 mW with 7.95% conversion efficiency at 94 GHz for 50% voltage modulation, peak RF power output and efficiency fall to 81.08 mW and 2.01% respectively at 0.5 THz for same voltage modulation. simulation results are compared with the experimental results and are found to be in close agreement.