Using a 2.45 GHz, 6 kW microwave furnace adapted for inert gas sintering, titanium diboride (TiB2) can be rapidly microwave-sintered to >90% of theoretical density with sintering temperatures of 1900 to 2100 °C and soak times of 30 min or less. Densification behaviour with low-level additives was evaluated; 3 wt% chromium diboride (CrB2) was an excellent sintering aid-grain growth inhibitor. A special covering system was required to produce oxidefree TiB2. Specimen surface and interior temperatures were determined with a “hole experiment”. Comparison with conventional sintering indicates that microwave sintering of TiB2-3 wt% CrB2 occurs at lower temperatures (i.e., 200 °C lower) and can yield material with improved hardness, grain size, and fracture toughness.