The concept of usability, which affects the quality and cost of the software projects, has become essential in recent years. There is a need to integrate usability testing activities and techniques into the development processes; however, integration is difficult. Therefore, this study proposes user-centered behavioral (UCB) software development model, which aims to bridge the gap between human-computer interaction (HCI) and software engineering (SE) disciplines. A triangulation methodology of mixed methods is used to understand the current situation in software development companies in terms of usability and user-centered software development by survey and interviews. Their results are then used to inform the development of the proposed model. The UCB software development model proposes a process in which several tools and techniques from SE and HCI are integrated to facilitate the production of highly usable software. In essence, the model proposes an iterative process that combines behavior-driven development (BDD)-an agile approach that enables a better understanding and analysis of the requirements-with the style guides, usability tests, heuristic evaluation, and Wizard of Oz techniques of HCI. The model was evaluated in a pilot project and then is improved based on feedback gathered. Participants' feedback supported the effectiveness of the proposed model.