A fundamentally new approach for synthesizing semiconductor nanocrystals - size-selectively - is described in this talk. Cadmium sulfide (CdS) nanocrystallites (NCs) have been synthesized on the atomically smooth graphite basal plane surface using a hybrid electrochemical/chemical (henceforth E/C) method. This method involves the following steps: 1) Electrochemical deposition of cadmium NCs onto an electrode surface, 2) Electrochemical oxidation of cadmium NCs to yield cadmium hydroxide (hexagonal) Cd(OH)@sub 2@ and, 3) Displacement of oxygen (or hydroxide) by sulfide either in the gas phase (via H@sub 2@S at 300 K) or in the liquid phase (using aq. Na@sub 2@S) solution. Electron diffraction is employed to monitor the progress of this synthesis, and the c rystal structures and orientations of the resulting nanocrystals which have mean diameters ranging from 30Å to 150Å. Wurtzite phase CdS nanocrystals generated by the E/C method possess the following characteristics: Single crystallinity, good-to-excellent si ze monod ispersity, epitaxial alignment (with the hexagonal periodicity of the graphite(0001) surface). In addition, E/C deposited particles on graphite exhibit strong room-tempera t ure photoluminescence (PL) spectra in which virtually no trap state emis sion is o bserved, and the energy of the emitted phonons is tunable based on the crystallite diameter. Extraordinarily good size monodispersity is possible for the CdS nanocrystals prepared by this method. One consequence is that the PL emission line widths seen for ensembles of 300,000 CdS nanocrystals can be as narrow as those seen for single CdS nanocrystals (15 meV at 20 K). V.