This paper presents recent results on highly integrated internally-matched Gallium Nitride transistors in S and C-band. The concept and the advantages of “Quasi MMIC” devices are described, showing the high potentialities for performance improvements and cost reductions. Using Gallium Arsenide based passive MMICs for input and/or output matching, more than 50W has been obtained at S-band with more than 55% PAE from 2.9GHz to 3.5GHz and more than 45% PAE at C-band @ 6.2GHz.