The study aimed to develop a cross-disciplinary integrative STEM (i-STEM) robotics curriculum by the thematic integration approaches of webbed and threaded models, and to understand high school students' cognitions, attitudes, and interests in robotics STEM after the instruction. The concurrent mixed methods including quantitative experimental design and embedded qualitative design were adopted in the present study. Participants were 42 students, with 17 females and 25 males in a high school class. The students were grouped with 2 members in each group, and there were totally 21 groups. The results revealed that cognition for seven fields were significantly improved. Among the seven fields, sailboat design improved the most, while mathematics and computer programming improved the least. The students' attitudes and interests in robotics STEM were significantly enhanced. The students' interests in engineering design were significantly enhanced the most, programming was the second; continuous study of engineering, science, or technology was the third; jobs related to engineering or programming was the fourth; and robotics was the least enhanced. Finally, the implications for teacher teaching and student learning practices were proposed.