High efficiency amplifier construction techniques are investigated focusing on UHF band transmitting power amplifiers intended for cellular portable telephones and the state of the art amplifiers are presented. First, it is shown that high efficiency amplifiers are indispensable to attain pocket sized portable units through a theoretical analysis using a simple model. When about 1 W of transmitting power is required, it is desirable for the amplifier to operate with an efficiency of over 40%. Secondly, the switching mode scheme is described as the most effective technical means to achieve high amplifier efficiency. State of the art switching mode amplifiers, the Harmonic Reaction Amplifier (HRA) and the Linearized Saturation Amplifier with Bidirectional Control (LSA-BC), are presented as examples of nonlinear and linear amplifiers respectively. Basic operation mechanisms are shown. Experimental HRA and LSA-BC are constructed to determine their practically attainable efficiencies. Power-added efficiencies of 75% and 40% are recorded from a 1.7 GHz band 3 W HRA for CW and a 1.5 GHz band 1 W LSA-BC for π/4 QPSK respectively. These values indicate that these types of amplifier can be applied to pocket sized portable radio units.