High-efficiency cw amplification with GaAs Schottky-barrier field-effect transistors under class-B conditions has been demonstrated. Power added efficiencies as high as 68% at 4 GHz and 41% at 8 GHz have been achieved. Two-tone tests were carried out at 4 GHz. The power added efficiencies at the 3rd-order intermodulation levels of minus 20, minus 25 and minus 30 db were 49, 40 and 35%, respectively.