This paper presents the design and analysis of a distributed power amplifier with 6-dB bandwidth from 10MHz to 6GHz. To meet the stringent targeted specification, the concurrent design and analysis are carefully performed with optimizations in both passive and active devices. The gate capacitive division technique is proposed and proven theoretically of bandwidth extension effect and power efficiency enhancement. To validate the theory, a prototype is designed in a 0.25-μm GaAs technology. The fabricated amplifier chip is packaged in an evaluation cavity of SMA connectors. The measurement shows an average power gain of 15dB, OP1dB and PSAT of 31dBm and 32.6dBm at 3GHz, and PAE at OP1dB and PSAT points are 31.5％and 43.7％respectively. To the best of authors' knowledge, the amplifier achieves the highest Power-added efficiency (PAE) among the similar GaAs amplifiers.