Abstract: As the key component of radio astronomy receiver system, the noise and gain performance of Low Noise Amplifier (LNA) have important influence on the sensitivity of receiver system. In this paper, a broadband LNA which can cover the C-band (4--8GHz) is developed by using the 100nm gallium arsenide (GaAs) pseudomorphic High Electron Mobility Transistor (pHEMT) technology. The amplifier adopts three-stage common source cascade amplifier topology and dual power supply structure. Measured results show that the average noise temperature of the amplifier is 60K in the frequency range of 4--8GHz with the lowest noise temperature of 50K being achieved at 5GHz. The gain is (31\pm1.5) dB in the whole bandwidth and the input and output return loss is better than 10dB. The chip area is 2.1\times1.1mm². This designed LNA can be used in the C-band radio astronomy receiver and satellite communication system.