It doesn't look like it. Searching for "Kalam" on http://www.admin.ch (which pruports to be the official site of the Swiss government) brings up one English result, "Indian President to visit Federal Institutes of Technology in Lausanne and Zurich". It is the press release for President Kalam's visit, dated 17 May 2005, nine days before the date in question. There is no mention of any "Science Day" in that article. Searching in French and German also returns one earlier, shorter press release (translated to each language), which also does not mention "Science Day". Searching the site for "science day" or "May 26" returns nothing. (Searching for "science" returns 250+ results, but since none of them mention Kalam, they are irrelevant.)
Furthermore, Science Day is not an official Swiss holiday. Per Wikipedia, there is only one federal holiday (i.e., declared by the Swiss national government): Swiss National Day, August 1. All other holidays are declared by the individual cantons. Wikipedia's list, which includes the holidays of the cantons, makes no mention of Science Day.
The claim is that Kalam visited CERN, so it might be asserted that the canton of Geneva, where CERN is located, declared the holiday (which would not be a Swiss holiday exactly, though it would still be true that it's celebrated in Switzerland); however, Geneva's own public holiday list has no mention of it. It seems unlikely that it would have been declared by one of the other cantons.
CERN has a list of official holidays, too. There is no Science Day, no mention of Kalam, no listing for May 26.
More circumstantial evidence is provided by TimeAndDate.com which has a list of all Swiss holidays and observances in 2005 and has no entry for March 26th.
Some light googling only comes up with repetitions of this claim, but no sources. If it were declared by Switzerland, we would expect Swiss record of someone declaring it; if it were celebrated, we would expect record of someone celebrating it. I have found none.