Ultherapy uses focused ultrasound to target the SMAS layer at about 4.5 mm...

https://tiny-wiki.win/index.php/Ultherapy_vs_Standard_HIFU:_What_Did_the_2024_Study_Say%3F

Ultherapy uses focused ultrasound to target the SMAS layer at about 4.5 mm deep, stimulating natural collagen over 3 to 6 months. Unlike RF, which heats skin to 40 to 45°C mainly in the dermis, Ultherapy reaches deeper for lifting