This work presents the design and implementation of a distributed gallium arsenide power amplifier (DPA) with integrated temperature and power sensing for high-power ultra-wideband applications, based on a 0.15-μm GaAs pHEMT process. The proposed amplifier consists of a distributed power amplifier (DPA), a temperature sensing unit, and a differential power detection unit. The distributed power amplifier adopts a cascode architecture, which significantly enhances the output power. The proposed temperature sensing unit employs a multi-point array-based temperature measurement scheme, in which different temperature sensing nodes can be selected through an external encoder. The differential power detection unit outputs detection voltages through the Vdet and Vref pins, effectively suppressing the influence of temperature variations on power detection accuracy. Measurement results indicate that, under the operating condition of Vgs = −0.5 V, the DPA achieves an operating bandwidth from DC to 28 GHz, with the output power (Pdc) increased to 30 dBm, a power-added efficiency (PAE) of 15%, and a gain flatness better than ±1 dB. Small-signal measurement results demonstrate that, over the operating bandwidth, both the input return loss (S11) and output return loss (S22) are better than −10 dB. The overall chip layout area is 3.8 mm × 1.5 mm.