Output power of HEMT
25 μm is the channel width, but 4 is not a 4-micron channel length. The phrase 4×25 μm ostensibly refers to four &quot;fingers&quot; of an interdigitated device(1), having a total effective channel width of 100 μm. Of course, since that's one-tenth of 1 mm, the power density and saturation power are consistent with each other now.
(1) - an interdigitated device is one where the structure is &quot;folded&quot;, e.g. the following simplified structure with two effective fingers: