A leading brand of heated tobacco products (HTPs), IQOS, was authorized to be sold in the United States in 2019. Researchers have examined the awareness and use of HTPs among US adults. In this study, we examined high school students' awareness, use, and susceptibility pertaining to HTPs. A large, cross-sectional population survey of randomly sampled 10th- and 12th-graders in California (N = 150 516) was conducted online during school hours from September 2019 to March 2020. Overall, 8.9% (95% confidence interval [CI], 8.7%-9.1%) of California high school students had heard of HTPs. Approximately 0.67% (95% CI, 0.61%-0.73%) had ever tried HTPs, and 0.20% (95% CI, 0.17%-0.23%) were current users (ie, ∼30% of ever users continued to use HTPs at the time of survey). Among those who never tried HTPs, 18.3% (95% CI, 17.9%-18.8%) were susceptible to future use. The susceptibility to HTP use was greater among users of cigarettes or e-cigarettes than among nonusers. The awareness of HTPs among adolescents was remarkable given the low availability of products at the time of survey. Only a small percentage of adolescents experimented with HTPs. However, almost a third of those who had experimented with HTPs continued to use them. This high ratio and the fact that almost 1 out of 5 never users were susceptible to future HTP use should put the public health community on high alert as more HTP products are coming into the market, with promotion of these products likely to increase.