This paper reviews the reliability problems of compound semiconductor devices. These devices suffer from specific failure mechanisms, which are related to their limited maturity. Only the GaAs MESFETs exhibit a stable technology and an assessed reliability. The metallizations employed in HEMTs already benefit from this assessment. However, HEMTs are affected by problems related to hot carriers and impact ionization, due to the high electric fields in the channel. The trapping of carriers and the generation of defects in the different layers are responsible for the observed instabilities. The stability of the base dopant is the main reliability concern for HBTs. The Be outdiffuses from the base to the emitter and causes degradation in the device performances. The C exhibits a lower diffusivity, but it is affected by the presence of H, which causes gain variations.