A method of forming an SOI fin using a porous semiconductor. The method may include forming a stack of semiconductor layers on a substrate, the stack includes a second semiconductor layer on a first semiconductor layer in a layered region; forming fins in the second semiconductor layer by etching a trench through an exposed portion of the of the second semiconductor layer; converting the first semiconductor layer into a porous semiconductor layer using a porousification process; and converting the porous semiconductor layer into an oxide layer.