Hardened programmable logic devices are provided with programmable circuitry. The programmable circuitry may be hardwired to implement a custom logic circuit. Generic fabrication masks may be used to form the programmable circuitry and may be used in manufacturing a product family of hardened programmable logic devices, each of which may implement a different custom logic circuit. Custom fabrication masks may be used to hardwire the programmable circuitry to implement a specific custom logic circuit. The programmable circuitry may be hardwired in such a way that signal timing characteristics of a hardened programmable logic device that implements a custom logic circuit may match the signal timing characteristics of a programmable logic device that implements the same custom logic circuit using configuration data.