This work presents a high-sensitivity shortwave infrared (SWIR) photoreceiver, designed using a high-gain In0.53Ga0.47As/Al0.85Ga0.15As0.56Sb0.44 Avalanche Photodiode (APD) with an extremely low excess noise factor of <3.5 at a gain of 100. The transimpedance amplifier (TIA) and input circuitry were rigorously optimized for precise APD gain control. Under investigation with APDs of 30, 80 and 200 μm active diameters, the receiver demonstrated a record-low room-temperature Noise Equivalent Power (NEP). An extremely low NEP of 21.2 fW/√Hz was achieved with a 30-μm-diameter APD, over a 440 MHz signal bandwidth, at an APD gain of 230 and the wavelength of 1550 nm. Current commercial APD-TIA modules typically exhibit NEPs of >100 fW/√Hz to 10's of pW/√Hz. Compared to its best- in-class 80-μm counterpart, this work's receiver demonstrated a 6.5× sensitivity improvement at 2× the operating bandwidth, with an NEP of 32.5 fW/√Hz. These results are of great significance for SWIR applications including extending the range of LiDAR systems, for which optimal performance requires the maximal- sensitivity detection of few-nanosecond optical pulses. The data reported in this article is available from the ORDA digital repository ( https://doi.org/10.15131/shef.... )