Yes, hotter than the sun’s surface, though not its core. According to the National Weather Service, a lightning bolt can heat the air it passes through to about 50,000°F, roughly five times hotter than the surface of the sun. NASA puts the sun’s visible surface, the photosphere, at about 10,000°F (5,500°C).
The sun’s interior is a different story: NASA says the core is about 27 million°F (15 million°C), far hotter than any lightning channel. Lightning only reaches its peak temperature for a tiny fraction of a second, and that sudden heating makes the air expand explosively, which is the sound we hear as thunder.
Source: National Weather Service, “Lightning Science Overview”; sun temperatures from NASA Sun Facts.
Image: “Lightning3.jpg,” U.S. Air Force photo by Edward Aspera Jr., public domain, via Wikimedia Commons.