Objectives Patients with high‐risk hematologic diseases require intensive modalities, including high‐dose chemotherapy and allogeneic hematopoietic stem cell transplantation (allo‐HSCT). Haploidentical T‐cell–replete transplantation is a logical choice because of the limited availability of matched sibling donors and the prolonged time needed to identify matched unrelated donors in Thailand. Methods The clinical outcomes data of 43 patients undergoing allo‐HSCT were reviewed. All patients had high‐risk hematologic malignancies, were younger than 20 years, and were in complete cytological remission at the time of allo‐HSCT. We used two different conditioning regimens: total body irradiation (TBI) combined with cyclophosphamide, fludarabine, and melphalan (n = 23) and thiotepa combined with fludarabine and busulfan (n = 20). All patients received a graft‐versus‐host disease prophylaxis regimen consisting of cyclophosphamide, mycophenolate mofetil, and a calcineurin inhibitor or sirolimus. Results There was no difference in engraftment between patients receiving either of the regimens. After a median follow‐up of 35.8 (range, 0.6–106.2) months, the overall survival (OS) and event‐free survival (EFS) rates were 62.4% and 54.7%, respectively. OS and EFS were comparable between the respective regimens. Conclusions We conclude that thiotepa‐based conditioning has similar efficacy and tolerability as TBI‐based conditioning for haploidentical HSCT with post‐transplant cyclophosphamide.