Recently, studies have demonstrated remarkable improvements in absorption spectroscopy of shallow impurities by using highly enriched $^{28}\text{S}\text{i}$ to eliminate the inhomogeneous isotope broadening inherent in natural Si. Here, we show that similar dramatic improvements in the linewidths of electronic transitions can be achieved with the two chalcogens sulfur and selenium in $^{28}\text{S}\text{i}$. The ${\text{S}}^{+}$ and ${\text{Se}}^{+}$ $1s({T}_{2})$ transitions exhibit a full width at half maximum of only $0.008\text{ }{\text{cm}}^{\ensuremath{-}1}$ for the ${\ensuremath{\Gamma}}_{7}$ component---more than one order of magnitude sharper than in natural silicon and a factor of 1.5 narrower than the width of the sharpest shallow impurity transition in $^{28}\text{S}\text{i}$. Hence they are the narrowest lines ever seen for impurity states in silicon. Fine structure is revealed in the absorption spectrum of the Se double donor and the ${^{77}\text{S}\text{e}}^{+}$ $1s({T}_{2})$ ${\ensuremath{\Gamma}}_{7}$ transition shows a splitting due to a hyperfine coupling with the $I=1/2$ nuclear spin. Under an applied magnetic field, the electronic, and nuclear spins can be individually determined with potential applications in quantum computing.