In the past few decades a big picture of low mass star formation has successfully been drawn. However, high mass star formation is little known yet, mainly due to its complexity, distance, and rarity. The Photodetector Array Camera and Spectrometer (PACS) on-board the Herschel Space Observatory (Herschel) has newly provided imaging spectroscopy with unprecedented angular resolution and sensitivity at far-infrared wavelengths. We present Herschel PACS data toward 10 high mass young stellar objects taken as part of the Water In Star-forming regions with Herschel (WISH) key project. In contrast to what has been thought, the preliminary results based on the continuum and CO lines show that hot molecular cores seem to have the highest extinction. It suggests that they are more deeply embedded compared to massive protostellar objects and ultra compact HII regions, which implies a very early stage of star formation.