Background and Objectives Data in literature regarding liver microwave ablation pertain to systems delivering 100 W of maximum power. Our aim is to assess a new 150 W microwave system for liver tumor ablation. Methods This was an institutional review board‐approved study of patients undergoing ablation of malignant liver tumors using a 150 W microwave system. Feasibility, safety, ablation algorithm, perioperative outcomes, and efficacy were analyzed. Comparison was made to historical patients undergoing ablation using a 100 W microwave system. Results There were 33 patients with 76 malignant liver lesions who underwent ablation with the 150 W system. Using a step‐wise algorithm, ablations without intraoperative complications were performed for tumors ranging in size from 0.3 to 6.7 cm. Ninety‐day morbidity was 5%, with no mortality. Compared to the 100 W system, the 150 W system shortened ablation time and created larger ablation zones with a single stick. Conclusion This first worldwide experience showed that surgical ablations could be safely created at 150 W using a step‐wise algorithm with complete tumor destruction achieved at short‐term follow‐up. Advantages versus 100 W systems include reduction in ablation time and creation of larger ablation zones with a single stick.