Radio frequency power amplifier is one of the essential modules in the transmission chain of wireless base stations. There is always a trade-off exists between power efficiency and linearity of the power amplifier. The design of power amplifier using LDMOS based active devices will give cost-effective solution. This paper presents the design of a class A power amplifier for unlicensed ISM band wireless base station requirements. The design is carried out using Si-LDMOS (Silicon - Laterally Diffused Metal Oxide Semiconductor) technology and is built on Epoxy-FR4 (Flame Retardant, woven glass reinforced epoxy resin) board with a dielectric constant of 4.6 and substrate thickness of 1.6mm.