Single pulse energies as high as 145 µJ were generated with a passively Q-switched diode-pumped Tm:KLu(WO4)2 laser using poly-crystalline Cr2+:ZnS as a saturable absorber. The maximum average power reached 0.39 W at a pulse repetition rate of 2.7 kHz with pulse durations in the 25 - 30 ns range. The maximum peak power amounted to 6 kW. The obtained results agree well with theoretical analysis.