Singapore has the second highest income gap between the rich and the poor, as indicated by the Gini coefficient, among the 38 countries with very high human development, according to the 2009 United Nations Development Report. Only Hong Kong has a higher income gap. See the table on this web page. You can also build your own tables using various economic indicators by going to the statistics page and you can read the report here.
The UN report says: The Gini index lies between 0 and 100. A value of 0 represents absolute equality and 100 absolute inequality.
Singapore, according to the 2009 UN report, had a Gini coefficient of 42.5, exceeded only by Hong Kong (43.4) among the countries with very high human development.
Here we compare Singapore's Gini coefficient with the figures for the rest of the 10-member Association of Southeast Asean Nations (Asean) and other countries with which it has close links. The figure tends to be lower in European countries, as this chart shows. All the figures are from the UN report.