Designing high power amplifiers at high frequencies is a great challenge, even at nowadays. I accepted this challenge when I started to write my thesis. My task was to design an amplifier to the 150-180 MHz frequency band, also called VHF (Very High Frequency) band that operates in class AB and its output power is at least 20 Watt. The reflection had to be stay under -15 dB and it had to run from an 50V power supply. To solve these problems, I used an LDMOS technology based high power transistor. In my thesis I will talk about the reason of my choice. I also mention the classic operation classes of amplifiers, like A and B, and the classic high frequency amplifiers with MOSFETs and bipolar junction transistors. I will also talk about the importance of the impedance matching networks. After the general things, I will present the design and build of my amplifier, the main steps, schematics, circuits and the results of the measurements. Finally, I publish my experiences and the bibliography.