In this paper a fully monolithically integrated power amplifier for X-band is presented. The push-pull amplifier uses an on-chip transformer for input matching, an autotransformer with capacitive divider for interstage matching, and an LC-balun for output matching. It does not require any external matching circuits. The power amplifier is implemented in a 0.35 μm SiGe bipolar technology. At 10 GHz operating frequency and a supply voltage of 1.5 V the amplifier achieves maximum power added efficiency greater than 30%, gain 23 dB, and maximum output power greater than 23 dBm.