We describe the design and results of a wide band C-X cryogenic IF amplifier developed for band 9 (602-720 GHz) of ALMA radio telescopes. A cryogenic 4-12 GHz isolator will be used at the input to improve matching. Several units have been fabricated and its results are presented. The amplifiers utilize HRL InP transistors to achieve a noise temperature of 5.3 K (0.08 dB NF) on average. Gain fluctuations are critical for the project.Values of Allan variance lower than 4.1 10-9 (0.1 s < T < 10 s) have been obtained.