In this paper, the effects of the applied electrical and magnetic field on the generation of optically induced terahertz (THz) electromagnetic radiation are reported by measuring the signal from the semiconductor emitter. The biased electrical field and magnetic field can enhance optically induced THz electromagnetic radiation. The emission spectra of time domain of semiconductors biased by applied electrical and magnetic field are obtained by the use of the reflection-type emitter irradiated by the femtosecond laser and the electro-optic sampling. The corresponding frequency domain spectra are obtained by fast Fourier transform (FFT). The results show that THz emission spectra are enhanced by the applied electrical and magnetic field, while their frequency components and bandwidths are not changed. By the classical electromagnetic theory, the effect of applied electrical and magnetic field on THz emission can be attributed to the acceleration motion of carriers in semiconductors.