An electric-motor assembly for installation in a borehole to power a downhole tools such as a pump has a first impermeable tube defining an axis and a stator fixed in the tube and having a series of coiled windings and laminations and electrically insulating potting in which the laminations and windings are imbedded. The windings have a connection to an electronically controlled power supply. An annular rotor in the tube radially surrounding the stator includes a permanent magnet coaxial with the windings. The tube seals the stator and rotor from the environment.