Combine the ginger and sugar, along with 1/2 cup water in a saucepan and bring to a simmer over a medium heat. Gently simmer the mixture, uncovered, until the ginger is tender, about 1/2 hour. Remove the ginger slices and place them on a sheet pan.
Return the saucepan to the heat and bring to a boil. Boil the syrup, uncovered, for 15 minutes, until the syrup is very thick.
Pour the syrup over the ginger slices and allow to dry, turning daily until the sugar crystallizes. Depending on the humidity, this may take several days.