ZURICH, May 4 (Reuters) - Swiss stock exchange operator SIX is adjusting its blue-chip SMI index family, capping the weighting of the largest shares at 18 percent as of Sept. 18, SIX said on Thursday.
Weightings of the top 20 Swiss stocks are to be capped at the quarterly index reviews, SIX said, adding a market consultation had revealed that issuers of financial products and users of index derivatives favoured such a change.
The amendment will be subject to transitional provisions, namely a gradual reduction in the weightings of the largest index components by 3 percent each quarter until they reach the required level, SIX said.
At the same time, a new index is to be launched with an identical composition to the SMI in which the weightings continue not to be capped, SIX said.
Nestle has the largest weighting now at around 22.6 percent followed by Novartis at 18.9 percent. No other stock has a weighting above 18 percent.
Reporting by Silke Koltrowitz and Oliver Hirt, Editing by Michael Shields