Semi-permanent tattoos do not exist. Tattoos are permanent. Tattoo ink is inserted into the dermis, or second layer of skin, and while it may fade with time, it never goes away.
Some unscrupulous tattoo artists claim they can tattoo the skin so lightly that their tattoos are semi-permanent, lasting only for six months to five years. These claims are all false. Any tattoos embedded into the epidermis, if such a thing were possible, would fade unevenly and incompletely. The only choices for non-permanent "tattoos" are temporary tattoos, which are essentially stickers on the surface of the skin and last up to a week, and henna body art, which lasts up to a month.