こんにちは @伶以 佐々木
英語でお答えします。
The Heatsink block (https://www.mathworks.com/help/sps/ref/heatsink.html) available from the library Simscape/Electrical/Passive/Thermal models a heatsink that dissipates heat from power semiconductors. "Fin height", "Fin thickness" and "Fin depth" are parameters whose value can be set in the block parameters (as shown in picture below) when "Parameterization" is set to "Assume rectangular parallel fins". These parameters however are not shown diagrammatically in the Heatsink block. The description of these parameters and the equation to calculate the dissipated heat is availabe here: https://www.mathworks.com/help/sps/ref/heatsink.html#:~:text=fin%20thermal%20conductivity.-,Parameterization%3A%20Assume%20Rectangular%20Parallel%20Fins,-If%20you%20set
Refer to this example (https://www.mathworks.com/help/sps/ug/optimize-inverter-liquid-cooling-system.html) which uses Heatsink block for better understanding of the component.
I hope this helps!