As part of Onsala Space Observatory instrumentation activities, a 4-8 GHz cryogenic low-noise amplifier was developed. This 2-stage LNA demonstrates 26 dB gain with noise temperature of 5.0 K using commercial GaAs transistors MGFC4419G from Mitsubishi. The total power consumption is of about 12 mW while with a total power consumption tuned down to 4 mW, the gain drops to 24 dB and the noise is of 6.0 K. This performance is in a very good agreement with simulations and believed to be among the best-reported using GaAs transistors. The amplifier design was carried using Agilent ADS, HFSS and Momentum CAD software. This amplifier will be used as a cold IF amplifier for mm and sub-mm wave receivers with SIS and HEB mixer, primarily for APEX Project as well in our development of ALMA band 7 sideband separation mixer providing two independent IF channels (USB and LSB) of 4-8 GHz, therefore fulfilling the 8 GHz bandwidth requirements for ALMA. In this paper we present details on the amplifier design, performances (modelled and measured) and gain-stability comparison between GaAs and InP transistor based amplifiers.