Semiconducting nanowire networks composed specifically of indium phosphide or silicon are developed with the goal of understanding their electrical, thermal and optoelectronic properties while developing scalable, manufacturable solutions to a number of problems of contemporary interest to society, with particular emphasis on direct conversion of heat to electricity. Nanowire networks are grown by metal organic chemical vapor deposition on non-single crystalline surfaces leading to highly interconnected networks of nanowires capable of long-range three-dimensional transport while retaining many of the unique properties of highly confined nanowire structures and displaying advantageous and unique properties such as mechanical flexibility. Growth of semiconducting nanowire networks is discussed in depth, especially relating to the role of the non-single crystalline surfaces from which they grow and morphological changes associated with doping. Finite element simulations suggest that the physical intersections present within a nanowire network are found to play a complex and potentially useful role in thermal transport and in electrical transport through experiment, demonstrating quantized conductance for the first time at room temperature. Electrical transport over distances far in excess of the dimensions of the individual nanowires is also studied experimentally by applying surface photovoltage techniques for the first time to nanowire networks. The theoretical model developed to analyze data from this, rst of its type, experiment reveals insights that can aid in developing improved thermoelectric devices. Such thermoelectric devices were fabricated using a highly scalable and very low cost approach. Thermoelectric testing displays large series electrical resistance but Seebeck voltages comparable to its bulk counterpart. The preliminary results clearly indicate that if series electrical resistance can be decreased, nanowire networks will be an excellent candidate for thermoelectric energy conversion materials.