Amoah was fourth behind American Erriyon Knighton, Jamaican Rasheed Dwyer and Nigeria’s Divine Oduduru.
Initially, his time looked good to secure him a final berth but the times produced in the other semi-finals ended his dream.
However, the 20.27 seconds is an improvement for Amoah, who clocked 20.35 in the heats.
Amoah must now focus on 4x100m relay in which Ghana, reigning African champions, are hopeful of taking a medal.
Ghana currently have one medal, a bronze won by 20-year-old boxer Samuel Takyi in the featherweight division.