In this paper, free standing beams and trench structures are successfully fabricated in both n and p-type silicon using macro-porous silicon. Electrochemical etching in hydrofluoric acid has been demonstrated to make 3-D structures in n-type silicon, in a single etch step. A set-up for n-type silicon involves a light source to generate electronic holes in silicon substrate, and the width of the pores can be controlled by the light intensity. However, the use of light makes the set-up more complicated. Using HF, p-type silicon was found only to form random micro-porous structures, and thus not the trenches achieved in n-type silicon. Recently, in order to form a macro pore in p-type silicon, a new etchant has been proposed in which the macro pores. This technique has been used to obtain macro-porous structures in p-type material. This technique has been extended to make free standing structures, as done with n-type material. This work has shown that free standing structures can be fabricated using a single etch step in both n and p-type material. P-type has the advantage that no light source is required and also thermal oxide can be used as a masking layer. However, experiments performed to date have shown that the n-type material process is easier to control and is more flexible, in terms of the structures which can be fabricated. Work is continuing to further improve these processes and this paper will examine the processes for n- and p-type material giving the relative merits.