A sample preparation method for transmission electron microscopy plan-views of InGaAsP/InP-based laser diodes based on selective chemical thinning is described. Using this method, it is possible to prepare samples with more than 50% of the active InGaAsP stripe electron transparent, The method is also comparably fast, simple, reliable, and will not introduce crystal defects in the sample. Examples of the use of this method for preparation of buried heterostructure laser diodes of bulk Fabry-Perot type are demonstrated. The technique is also applicable. to other types af laser diodes, such as multiquantum wells and distributed;feedback.