There is critical clinical demand for tissue-engineered (TE), 3D constructs for tissue repair and organ replacements. Current efforts toward this goal are prone to necrosis at the core of larger constructs because of limited oxygen and nutrient diffusion. Therefore, critically sized 3D TE constructs demand an immediate vascular system for sustained tissue function upon implantation. To address this challenge the goal of this project was to develop a strategy to incorporate microchannels into a porous silk TE scaffold that could be fabricated reproducibly using microfabrication and soft lithography. Silk is a suitable biopolymer material for this application because it is mechanically robust, biocompatible, slowly degrades in vivo, and has been used in a variety of TE constructs. Here, the fabrication of a silk-based TE scaffold that contains an embedded network of porous microchannels is reported. Enclosed porous microchannels support endothelial lumen formation, a critical step toward development of the vascular niche, while the porous scaffold surrounding the microchannels supports tissue formation, demonstrated using human mesenchymal stem cells. This approach for fabricating vascularized TE constructs is advantageous compared to previous systems, which lack porosity and biodegradability or degrade too rapidly to sustain tissue structure and function. The broader impact of this research will enable the systemic study and development of complex, critically-sized engineered tissues, from regenerative medicine to in vitro tissue models of disease states.