An investigation on the effect of TMAH concentration on the etch rate of silicon, and the influence of etchant concentration, ambient temperature and wafer thermal history on the formation of pyramids at the surface of TMAH etched silicon has been carried out. From the results obtained from this study, we are able to explain the influence of TMAH concentration and ambient temperature on the silicon etch rate and the changes occurring at the silicon surface satisfactorily using the pH theory. However, the results from wafers with different thermal history seem to favour the defects theory. We suggest that in order to explain the etching mechanism of TMAH of silicon satisfactorily, a combination of pH and defects theories is necessary.