At 2.45pm, the Swiss currency stood at 1.219 francs against the euro -- a high since the end of November -- compared to 1.2204 late on Friday.
The franc rose swiftly last Thursday after the decision of the Swiss National Bank to continue to enforce its minimum exchange rate of 1.20 franc per euro, imposed at the beginning of September to hold the Swiss currency down and support exports.
The SNB said it was prepared to take further measures, including buying "unlimited" foreign currency if necessary.
Analysts at the Zurich Cantonal Bank said the "lateral" movement of the franc would continue for several weeks.
But if the Swiss currency should near the 1.20 limit against the euro, the SNB would intervene, they said.