Thermal throttling is a fact of life for smartphones. SoCs generate a lot of heat, and when this heat can't be dissipated, processors react by slowing down and thereby generating less heat. Usually this is just an issue for heavy 3D gaming sessions or a phone directly exposed to sunlight for a long time, like when mounted on a car windshield. In the era of 5G, though, heat is also an issue for your modem.

While the vast majority of people don't yet have access to a 5G phone or 5G service, PCMag's Sascha Segan has been flying around the country testing out the carriers' nascent implementation of 5G. So far, the heat generated by Qualcomm's first-generation chips is an issue. Segan writes:

On a hot Las Vegas morning, my two Galaxy S10 5G phones kept overheating and dropping to 4G. This behavior is happening with all of the millimeter-wave, first-generation, Qualcomm X50-based phones when temperatures hit or exceed 85 degrees. We saw it with T-Mobile in New York, with Verizon in Providence, and now with AT&T in Las Vegas. It's happened on Samsung and LG phones, with Samsung, Ericsson, and Nokia network hardware.

As we wrote back in December, Qualcomm's first-generation 5G design is a significant regression from the fully integrated 4G chips we've been used to. A modern 4G LTE smartphone packs everything into a single main chip, which houses all of the usual computer components along with the LTE modem. Today's 5G design requires that same chip, along with a separate chip for the 5G mmWave modem and several more chips for the mmWave antenna modules. The result is that 5G takes up a lot more space and generates a lot more heat than 4G, and when this heat gets to be too much, all that 5G circuitry just shuts off.

Overheating in 85-degree weather sounds a lot more excessive than the heat issues from an extended gaming session. The 5G modem will be on any time you're simply browsing the Web or doing anything on the Internet, so it sounds like 5G users would run into heat issues more frequently than a mobile gamer. Segan doesn't sound too happy about the heat issues either, saying, "This persistent overheating behavior just makes me more confident in recommending that consumers wait to buy a 5G phone."

To make matters worse, some carriers don't even report when this is happening. Segan writes "AT&T being AT&T, the company leaves the "5G+" indicator on the phone even when it's dropped to 4G from overheating." AT&T has been working overtime this year to remove all meaning from the term "5G" by rebranding its 4G service to "5G Evolution," but "5G+" on an AT&T phone is supposed to actually mean you're getting 5G mmWave service. Showing customers a 5G indicator and then giving them 4G speeds will certainly cause confusion, but that ship sailed for AT&T customers long ago.

This overheating news is the latest piece of evidence to scream "Don't buy a 5G phone." The devices are bigger, hotter, more expensive, and have less battery life than their 4G counterparts. Service is only available in a handful of cities, and even when you are in those cities, 5G coverage is limited to certain blocks. Now comes the news that even when you have compromised your device with 5G hardware and stand at the right address, you might not even get 5G if it's hot out.