The paper reports the first test results of a new High Efficient Multistage Plasma thruster (HEMP thruster) concept, unique by its potential for extremely low wall losses and low sputter erosion, its high thrust densities and extremely wide operational ranges. The highest thrust and thrust density (thrust per channel exit area) of 43 mN and 16.9 mN/cm2 were measured so far with demonstrator model DM3a MS2 on the thrust balance of ONERA in July 02 at 30 sccm Xe flow, 500 V and 2.88 A, respectively. This operational limit was not set by the device, but the limited test time and power supply capabilities. At the same test campaign another demonstrator model DM3a MS1-2 having a slightly lower apparent ion beam angle and delivering a thrust of 24 mN provided within the smaller operational stability range the best combination of total efficiency and specific impulse with 31% and 1682 s, respectively, at a Xe flow of 15 sccm, an anode voltage of 550 V and an anode current of 1.16 A. For brevity, the details are not given here. A further improved version, DM3a MS1-3, was tested in Oct. 02 at IOM at Leipzig with respect to angular and energy distribution of the ion beam at one selected operating point of 8 sccm, 500 V and 0.505 A. The performed measurements provided insight into the distribution of the multistage plasma potentials and the ionisation probabilities inside the thruster channel and confirmed the ideas the HEMP thruster concept is based upon. The integration over the angular and the energy distribution resulted in a thrust value of 12 mN, a total efficiency of 38% and an effective swallow tail beam angle of 43°. Another surprising feature of DM3a MS1-3 has been its ability to turn on and off the neutraliser cathode with practically no impact on the thruster operational characteristics and its performance. At present a new HEMP thruster layout DM6 is under test. Current measurements on DM6 MS1 performed at TED Ulm by means of an own developed thermal diagnostic indicated further significant improvements. At 14 sccm, 600 V and 1.3 A, thrust, total efficiency and specific impulse were determined to be well above 30 mN, 55 % and 2300 s, respectively. For Xe flows up to 8sccm DM6 MS1 could be stably operated at anode voltages of up to 1800 V, providing specific impulses well above 3500 s. Also operation of DM6 MS1 required no neutraliser cathode. It is intended to confirm these thermal diagnostic results on DM6 versions in the course of thrust balance tests to be performed at ONERA in February 03 the results of which shall be presented at the conference.