Clumpy irregular galaxies are made up of 5-10 bright clumps loosely scattered in a common envelope, have excess near-UV radiation and are giant compared with classic irregular galaxies1,2. Clumps are apparently ~100 times more massive than giant H II regions such as 30 Doradus or NGC604 (ref. 3). To get an insight into their properties we have obtained UV spectra using the IUE satellite of one of the clumpy irregular galaxies, MKN297. The UV continuum spectrum thus obtained follows a power law and is steeper (fainter at short wavelengths) than that of a classic irregular or late galaxy. The 155 nm intrinsic luminosity is 400 times larger than that of 30 Doradus. The observed absorption lines can be attributed to early O or B stars, and no emission lines are detectable. We report here that the spectra indicate that each of the clumps contain ~104 early stars and are supergiant H II regions in which exceptional bursts of star formation take place.