It is a BJT (bipolar junction transistor), NPN type, based on all available measurements.
: Typically rated with an access time of 70ns (indicated by the "-70" suffix in its equivalent part number). Application & Repair nec b58944 datasheet 2021
The 2021 datasheet emphasizes the device's switching efficiency, a critical parameter for modern SMPS (Switched-Mode Power Supplies) and DC-DC converters. It is a BJT (bipolar junction transistor), NPN