Windows NT Kernel is not a microkernel by nature. However, it's design is layered, and what runs in privileged mode (i.e. the kernel) is divided into the Kernel (note the lettercase), the Executive and (Device) Drivers. The Kernel implements core operating system functionality and is platform dependent. The Execute layer is build on top of the Kernel and provides a set of core services of various Windows NT Kernel sub-systems (such as Virtual Memory Manager, Object Manager, Configuration Manager, ...). Drivers are kind of kernel-mode services which need to run in privileged mode (such as device drivers) and use Kernel and Executive services. Also, user mode API libraries (NTDLL, Win32 API, ...) interface with Executive services to do their job.

Whether the NT Kernel is a microkernel or not is a common topic of arguments among system engineers ;).