Electronic device with thermal management system

An electronic device may have electrical components that produce heat during operation. An electronic device may also be heated by sunlight incident on the device. A thermal management model may take into account device structures such as housing materials in modeling the thermal behavior of the device. Temperature sensors in the device may be used to measure internal temperatures. The model may use temperature measurements and other data such as environmental data measured with sensors in predicting temperatures for one or more regions in a device. In response to prediction of a temperature greater than a predetermined threshold, the device may take remedial action to avoid overheating. Remedial action may include adjusting electrical components so that they produce less heat, activating a heat blocking component such as an electronic shutter, and reducing communications activity levels and other software activity levels.