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A high-gain matrix distributed amplifier (DA) was developed using a commercial GaAs PHMET foundry for 40-Gb/s baseband applications. Two tiers of matrix DA are directly coupled using a lumped DC level-shift circuit. The DC bias level of the second tier can be tuned using the level-shift circuit for optimum gain. The gain of the matrix DA has been optimized using an active feedback cascode topology, which allows the gain-bandwidth product (GBWP) to be maximized while avoiding instability problems. In order to improve the gain, the second tier is shifted to the output load. The fabricated single-chip matrix DA with a size of 2.4 mm × 1.4 mm showed a high gain of 19 dB, and an average noise figure of 5.7 dB with a 48-GHz bandwidth. The GBWP is 428 GHz, which corresponds to the highest performance using GaAs technology for matrix DAs.