Serious Drug Offender Death Penalty Act of 1988 - Amends the Controlled Substances Act to provide for a mandatory death penalty for: (1) the murder of a law enforcement officer during the course of a Controlled Substances Act violation; (2) certain violations involving ten or more kilograms of heroin, cocaine (including cocaine freebase), phencyclidine, or a controlled substance analogue; (3) second or subsequent violations involving one or more kilograms of such substances; (4) using a firearm in the commission of certain violations involving one or more kilograms of such substances; or (5) violations involving one or more kilograms of such substances when, as a result of the violation, such substances are obtained by a minor.