The computational part is no different from any other ASIC, just set down the exact transistors you need to do the same algorithm over and over.

What makes ETH asic resistant is its dependency on random memory access. There is no way to speed up this part, an ETH ASIC would have to use the same memory chips as computers.

Turns out this wasn't as big of an obstacle as people thought though, GDDR5 chips are expensive but there are mountains of DDR3 chips laying around for a cheap price. Since the algorithm scales perfectly in parallel, there is no reason why these slow DDR3 chips can't be used en masse to provide the required memory for ASIC's.