STEAM education integrates science, technology, engineering, arts, and mathematics to foster interdisciplinary learning and support the development of 21st-century skills. However, implementing this approach requires the development of educational resources that meaningfully connect these disciplines. Augmented Reality (AR) can contribute to this effort by enabling interactive and immersive learning experiences. This paper presents AR-GenSTEAM, a generator for creating STEAM-based serious games with AR for web and mobile platforms. The generator follows a three-stage development process comprising analysis, configuration, and generation. Through this process, users select STEAM areas, target skills, game templates, AR resources, and an export platform to generate a serious game. A case study of Enkrypto, a serious game focused on encryption and decryption, is presented to illustrate the use of AR-GenSTEAM. A hybrid evaluation was conducted to evaluate the performance of AR-GenSTEAM and students’ experiences with the AR component of the Enkrypto game. The generator successfully generated web applications in 90% of attempts and mobile applications in 80%, while students rated the AR component positively in terms of pragmatic quality, hedonic quality, and overall user experience.