The average surface temperature of Venus is about 464 °C. That makes Venus the hottest planet in the Solar System, even though Mercury is closer to the Sun.
The extreme heat comes from Venus's thick atmosphere, which is composed mostly of carbon dioxide. This gas traps infrared energy in a powerful runaway greenhouse effect. Heat is distributed around the planet by the dense atmosphere, so temperatures remain extraordinarily high even on the side facing away from the Sun.
Venus's surface pressure is about 92 times Earth's sea-level pressure, comparable to the pressure nearly 1 kilometre beneath Earth's oceans. The temperature is hot enough to melt lead. A common mix-up is to assume Mercury must be hottest because it receives more sunlight; Mercury has almost no atmosphere, so its nights cool sharply, while Venus retains heat globally.