In most short-range wireless sensor network applications, the maximum transmit-power is typically about 10dBm at 2.4GHz ISM band. In such a low transmit-power level, the driving power and DC power consumption in the previous stage are no more negligible compared to the transmitted signal power. So, to increase the overall transmitter efficiency, not. only the output power stage, but the driver stage needs to be co-optimized for low power Operation. In this paper, we present an injection-locked Class-E power amplifier (Class-E ILPA) suitable for the low transmit-power sensor network applications. The proposed power amplifier, which is fully integrated in 0.18μm CMOS technology, achieves a power added efficiency (PAE) of 43% while delivering an output power of 9.5dBm with a drain efficiency(DE) of 48.5% at IV supply voltage.