Colloidal semiconductor nanocrystals (NCs) are promising building blocks for various electronic and optoelectronic applications such as light emitting diodes, solar cells, field effect transistors (FETs) and more. Their functionality in such scenarios benefits from the compatibility with bottom-up device fabrication methods practiced in the general field of “printed electronics”, accompanied by the high tunability of their properties afforded by size, shape and composition control. Control over the charge carrier type and concentration in a semiconductor is a critical step for tailoring the optoelectronic properties of a device and can be achieved by the process of doping. We have been working on the different mechanisms of doping namely, laser induced doping, diffusion doping and thermal doping. However, impurity doping, which is the most common process in bulk top-down fabricated semiconductor devices to tune their optoelectronic functionality, still presents major challenges in semiconductor nanocrystals based devices. We study the scientific basis of impurity doping of Colloidal NCs in order to control the carrier type and concentration in bottom-up fabricated electrical devices such as thin film FETs. As a model system for impurity doping we use InAs nanocrystals where we have recently demonstrated control over the carrier type and concentration in electrical devices.