Digital technology propels online teacher professional development (TPD). While offering convenience, the introduction of online technology also exerts certain pressures on the online TPD, and different online educational technologies influence the effectiveness of teacher training. The gap in learning outcomes, when different teachers use online training technologies, remains to be investigated. This study adopted cognitive load to examine the effectiveness of online TPD, detecting the differences in extraneous cognitive load (ECL) and germane cognitive load (GCL) among 76 STEM teachers and 76 Chinese language teachers in online learning supported by three online technologies: pre-recorded videos, live lectures, and AI chatbots. The results indicate that STEM teachers exhibit a lower ECL when applying to pre-recorded videos and live lectures compared to Chinese language teachers. Meanwhile, there is no significant difference in ECL when using AI chatbots. The findings suggest that online professional training for teachers of different disciplines could adopt more fitting and personalized online technologies.