High-output-power and high-bandwidth performances are usually two tradeoff parameters in the design of high-speed photodetectors. In this letter, we report high peak-output-voltage (∼20 V) and peak-output-current (∼400 mA, 50 Ω load) together with ultrahigh-speed performances (1.5 ps, 220 GHz), observed in low-temperature-grown-GaAs (LTG-GaAs) based metal-semiconductor-metal (MSM) traveling-wave photodetectors (TWPDs) at a wavelength of 800 nm. Ultrahigh-peak-output-power and ultrahigh-electrical-bandwidth performances were achieved due to the superior MSM microwave guiding structure and a short carrier trapping time in the LTG-GaAs layer, which reduced the space-charge screening effect and increased the photoabsorption volume without sacrificing electrical bandwidth significantly. We also observed different bias-dependent nonlinear behaviors in MSM TWPDs under high and low illuminated optical power excitations, which are possibly dominated by the space-charge screening and the lifetime increasing effects, respectively. © 2002 American Institute of Physics.