Compound semiconductors like gallium arsenide yield high switching speeds for logic applications. Velocity saturation values of 1.2 and 1.8 × 10/27cm/s at room temperature occur in GaAs for ordinary doped-channel MESFETs and modulation-doped heterojunction FET's respectively. Sub-half-micron GaAs devices are shown to have 4.0 and 8.0 × 107cm/s velocity values for gradual acceleration and quick acceleration respectively. These high velocity values, yielding high gm values, are possible with low voltage swings. These allow very high switching speeds. To date 15 psec switching with doped-channel MESFETs, and 12 psec with modulation-doped FET's have been obtained with unity fan out at room temperature respectively. The latter device is expected to switch in less than 5 psec for shorter drift distances. The physical electronics of the various structures, and some the technologies used for growing and processing devices will be presented.